The dynamic response of a rear suspension system to the multitude of loads imposed upon it during operation is undoubtedly one of the most critical factors in determining the overall performance and ride comfort of a tracked vehicle such as a snowmobile. A rear suspension system generally has to contend with three types of loads that are regularly exerted upon a tracked vehicle regardless of whether it is employed for racing or mere recreation. First and foremost in severity are the impact loads imposed upon the rear suspension as the vehicle traverses rough terrain and encounters bumps. Secondly, there are internal forces developed during rapid acceleration which cause a weight transfer from the front of the vehicle to the rear. This tends to lift the skis off the ground and thus hampers steering. Finally, there are centrifugal loads imposed on the vehicle when cornering at high speeds. The complex interaction of the forces developed in the rear suspension system especially during vigorous operation have compelled engineers to re-evaluate the simple, traditional spring-damper mechanisms used to absorb shocks and to design new optimal (i.e. weight and cost-efficient) mechanisms for absorbing and attenuating the complex combination of loads imposed upon a modern high-performance snowmobile. Besides the force, stress, strain and fatigue considerations, suspension engineers have had to contend with the additional constraint of space. In order to improve cornering performance, snowmobiles must maintain a low center of gravity. This means that the suspension must be as compact as possible when fully compressed.
The fundamental structure of the rear suspension of a tracked vehicle such as a snowmobile has remained essentially constant for many years now. The rear suspension supports the track, which is maintained tout around a pair of parallel rails, a multitude of idler wheels and at least one drive wheel or sprocket. A shock absorbing mechanism involving compressed springs, dampers, struts, shock rods or practically any combination thereof urges the slide frame and the chassis of the snowmobile apart. In static equilibrium, the force of the springs urging the slide frame and the chassis apart is equal and opposite to the weight supported above the suspension. In recent years, engineers have begun to produce advanced suspension systems wherein the damping, spring rate, and range of travel can be adjusted to limit internal weight transfer caused by track tension and to improve comfort, control and performance.